1. Field of the Invention
The present invention relates to hard disk drives. More particularly, it relates to a disk drive spindle motor including a wire guide insert for facilitating rapid assembly at reduced costs.
2. Description of the Prior Art and Related Information
A huge market exists for mass-market host computer systems such as servers, desktop computers, and laptop computers. To be competitive in this market, a hard disk drive must be relatively inexpensive and must accordingly embody a design that is adapted for low cost mass production. Numerous manufacturers compete in this expansive market and collectively conduct substantial research and development, at great annual cost, to design and develop innovative hard disk drives to meet increasingly demanding customer requirements.
Each of the various contemporary mass-marketed hard disk drive models provides relatively large data storage capacity, often in excess of 1 gigabyte per drive. To this end, there exists substantial competitive pressure to develop mass-market hard disk drives that have even higher capacities and that provide rapid access to stored data. Another requirement to be competitive in this market is that the hard disk drive must conform to a selected standard exterior size and shape often referred to as a "form factor". Generally, capacity is desirably increased without increasing the form factor, or the form factor is reduced without decreasing capacity.
Satisfying these competing constraints of low-cost, small size, high capacity, and rapid access requires innovation in each of numerous components or subassemblies. Typically, the main subassemblies of a hard disk drive are a head disk assembly and a printed circuit board assembly.
The head disk assembly includes an enclosure including a base and a cover; at least one disk having at least one recording surface; a spindle motor causing each disk to rotate; and an actuator arrangement. The actuator arrangement includes a separate transducer for each recording surface, and is movable to position each transducer relative to the recording surface. The printed circuit board assembly includes circuitry for processing signals and controlling operation of the drive.
A disk drive spindle motor typically includes a base, a central shaft, an upper bearing, a lower bearing, a stator and a rotor (or "hub"). The hub normally forms a flange to which the disk(s) is attached. The shaft is attached at one end to the base. The hub is concentrically positioned about the shaft. To this end, the upper and lower bearings maintain the hub in this concentric position such that the hub is rotatable about the shaft. The stator includes a series of coils or wires wrapped around a core and is concentrically positioned about the shaft, adjacent the hub. Leading portions of the stator wires extend downwardly from the core and are electrically connected to the printed circuit board assembly. With this general configuration, the various coils of the stator are selectively energized, via signals from the printed circuit board assembly to form an electromagnet that pulls/pushes on a magnet otherwise associated with the hub, thereby imparting a rotational motion onto the hub. Rotation of the hub results in rotation of the attached disk(s).
Several different disk drive spindle motor designs are currently available, each conforming generally with the basic description provided above. For example, one design is referred to as a "top-down" spindle motor. The top-down spindle motor design includes a stator sized to be concentrically positioned about the lower bearing. In other words, the stator has an inner diameter greater than an outer diameter of the lower bearing. The hub forms a slot within which the stator is disposed such that the hub is directly secured to the upper and lower bearings. Notably, during assembly of a top-down spindle motor, the stator wires are readily directed from the stator core to the printed circuit board assembly in that no rotating parts, such as the lower bearing and the shaft, present an obstacle to desired positioning.
In addition to the top-down spindle motor design, other spindle motor configurations have been devised to satisfy certain performance enhancements. For example, the overall data storage capacity of a disk drive can be increased by adding additional disks beyond the number typically found with a top-down spindle motor. Further, it may be necessary to increase the rate at which the hub (and therefore the disks) rotate. To accommodate additional disks, a hub that is taller than that normally associated with a top-down spindle motor is required. Unfortunately, the top-down design may not provide sufficient motor volume to drive an elongated hub with multiple disks. To resolve this potential problem, a "split bearing" spindle motor has been engineered.
The split bearing spindle motor is generally similar to the top-down design. As the name implies, however, the split bearing design positions the stator directly between the upper and lower bearings, as opposed to outside of the lower bearing. The upper bearing, stator and lower bearing are effectively aligned along the shaft, and surrounded by the hub. This approach allows for an increase in motor volume for a taller hub so that additional disks can be mounted to the hub. Further, the split bearing design has proven to be stable at increased rotational speeds.
The split bearing spindle motor design is generally more expensive than a top-down spindle motor due, in part, to certain manufacturing issues. For example, as previously described, during assembly, leading portions of the stator wires must be directed downwardly from the stator core to the printed circuit board assembly for requisite electrical connection. Unlike the top-down design, with a split bearing spindle motor, the hub, lower bearing and shaft present a physical barrier to extension of the stator wires. Because the stator is positioned directly above the lower bearing, the hub and lower bearing obstruct a direct path from the stator core. A solution to this problem is to gouge a slot into the shaft adjacent the lower bearing. The stator wires are then passed around the lower bearing via the slot. Notably, the stator wires cannot be passed through the hub and/or the lower bearing as they are both rotating parts. The slot is normally formed by a machining operation and the stator wires are manually fed through the slot; the manual feeding of the stator wires through the slot is labor intensive and is therefore relatively expensive in terms of mass production. An additional manufacturing concern resides in the fact that a fast-drying adhesive is normally used to secure the lower bearing to the shaft. Thus, if any difficulties are encountered in maintaining the stator wire within the gouged slot during assembly of the lower bearing to the shaft, the adhesive may not set properly, rendering the motor unusable. Finally, imparting a slot into a high precision item such as the shaft may cause increased vibration of the shaft as a result of the slot decreasing the stiffness of the shaft.
U.S. Pat. No. 5,173,814 ("the '814 patent") discloses one alternative way of solving the stator wire guide problem associated with assembly of disk drive spindle motors. The '814 patent provides in one instance forming a passage in the shaft through which the stator wires are guided to the printed circuit board assembly. In a second instance, the '814 patent describes use of a bearing support ring having an internal bore. The bearing support ring is secured between the lower bearing and the shaft. With this configuration, the stator wires must be manually fed through the internal bore in the bearing support ring. Because the stator wires are quite thin and relatively flexible, it is likely difficult to thread the stator wires through the bore in an expedited fashion. Additionally, due to space limitations between the stator and lower bearing upon final assembly, it would be difficult to feed the stator wires through the internal bore once the support ring has been secured to the shaft.
Accordingly, substantial research and development efforts have been expended to provide an improved spindle motor design that facilitates rapid assembly while minimizing manufacturing costs and which maintains sufficient stiffness in the spindle motor shaft.